In the course of manufacture of certain electrical devices, such as hybrid integrated circuits, it is often necessary to mount a plurality of components or chip carriers on one surface of a thin film ceramic substrate. These chip carriers may be attached to the substrate by as many as 32 solder joints. The solder joints, which support the respective chip carriers above the surface of the substrate, establish an air gap between the carriers and the surface of the substrate. The air gap permits the flow of cleaning fluids to remove solder flux that may be present under the chip carriers which would cause leakage currents when high voltages are applied to the substrate. Moreover, the air gap facilitates the encapsulation of the solder joints. The presence of the air gap makes the alignment of the chip carriers with appropriate ceramic substrate pads a difficult task. Thus, each solder joint must be visually inspected for misalignment, shorts between adjacent joints and missing solder joints in order to reduce subsequent costly test diagnostic time of defective circuits.
One method of inspecting the solder joints involves a free-hand rotation of the hybrid integrated circuit beneath a microscope. This method is very cumbersome because each chip carrier must be rotated four times and the location of the defective component or chip carrier must be noted for subsequent repair. This process is difficult to perform without mistakes because the orientation of the circuit is attained by manual manipulation in space. Moreover, it is further complicated by (1) closely spaced adjacent components which block the view of the solder joints or (2) the necessary and repeated steps of looking back and forth between the microscope and documentation which identifies the defective component or chip carrier's location. The process is very time consuming and causes eye fatigue because of the varying focal lengths due to an unsteady hand.
Consequently, an apparatus is needed which can be rapidly operated to accurately fix the orientation of the circuit at a constant focal length from the microscope and allows the inspection of solder joints at varying distances beneath the component or chip carrier.